The 6 foot dish dilemma

[ikki]

As some of you know my first C Band dish was a 6 footer that I got for free.

Since 2007 I have messed around with it and have determined that it is pretty much worthless for C band.

Last fall I installed a prime focus KU band LNBF and it mostly made it though the winter but was only being held in by "tape".

I have looked around around for a better mount and have been unable to find one. So I am left with two options.

1. Give the dish away for free with LNBF (C or KU) and wash my hands of it.

2. Figure out a way to mount this KU LNBF correctly.

Any thoughts?

Here is an older thread with a picture of my dish.

http://www.satelliteguys.us/4dtv-discussion/176144-w5-4dtv.html

(You will notice the LNBF is supported by four arms instead of the usual three)

 

[Tron]

The 6 foot solid panel dishes are quite useful for C-Band, if somewhat weak or problematic on DVB-S2 transponders. There is a Ku-Band LNBF holder for BUDs, but the holder is designed for a dish with three support poles, not four. Since it is a mesh dish, you might want to disassemble and store it as a spare. It shouldn't take up much room, and you can look for a larger mesh dish for C-Band.

 

[turbosat]

Ikki have you tried a little fabrication on an old prime focus c-band feedhorn. The flange on some of them had pre-drilled holes for 4 support arms. This is not something I have tried yet, but only because I found it easier to get reliable ku from a dish made for ku, like those Channel master-primestar dishes. I have a 5' alum dish made for c-band, that I tried to get good ku from, for several months. Actually had it tracking pretty good too, but when I got my first primestar and connected it-the difference in signal was amazing. So I never went back to primefocus dish for ku, though some folks have great success with them.

 

[yankee495]

I had a 6 foot ring mount dish with no support arms at all. I used conduit and conduit clamps to make adjustable arms for it. Worked very well and was cheap. I figured the focal distance of the dish and bought 4 or so more inches than I needed for each arm.

By lengthening one arm and shorting another I could adjust center. Lengthen/shorten all 3 and you could adjust focal distance. It was a pain to get right (close), but you had all of the adjustment you needed!

Once you got close it was pretty easy to get peak signal. I used a Sharpie marker to put lines on the arms that were close. Then tighten them just far enough to still move them. This was in the analog days and "sparkelies". Use whatever size conduit you need, hammer one end flat for a few inches, bend it to the right angle and drill a hole to mount to the scalar ring.

Then use these clamps:

lowes.com/pd_75308-15527-49110_0__?productId=1100127&Ntt=conduit+clamp&pl=1&currentURL=%2Fpl__0__s%3FNtt%3Dconduit%2Bclamp&facetInfo=

Measure to find their position, drill holes and mount them. The position can be off a little because you have full adjustment for center and focal distance.
It worked very well, was cheap, adjustable and looked good. It also held tuning very good as it was bolted!

 

[ikki]

> ...but when I got my first primestar and connected it-the difference in signal was amazing. So I never went back to primefocus dish for ku, though some folks have great success with them.

One last question. Is the general consensus on this board that 3 foot / 4 foot KU band offset dish will always outperform a 6 foot prime focus dish that was ment for C band and converted to KU band?

I realy need to figure out what to do before winter

 

[FaT Air]

I'd think that a 1.2m (1 piece) offset would out perform a 2m (multi-panel) prime focus consumer dish on the Ku band. Unless your willing to put in the effort and time to get everything just right (perfect), Also, the feed used could effect performance greatly. A re-purposed commercial offset would be even harder to out perform. Basically saying, the 1.2 should outshine the prime focus with equal labor. (Investment $ could go either way depending on how acquired) BTW- these are only my thoughts, I've never messed with a 6ft on Ku to compare performance of the two, side by side. Maybe should have started a poll?

 

[ikki]

If you do not mind starting a poll asking that question that would be awesome.

 

[pendragon]

If you're looking for Ku-band reception, I would dump the 6' and go with a good 1.2m offset (SatelliteAV has very a very nice unit, but shipping is costly). It's a very rare FTA prime-focus dish that can beat a 1.2m offset on Ku. A prime-focus' surface accuracy is usually not adequate and finding a LNB(F) that matches is not easy. I have looked at "prime-focus Ku LNBFs", but have reservations. They tend to be specified with a f/D of 0.5-0.7, which will horribly under-illuminate any prime-focus dish. However pictures suggest their actual f/D may be lower.

I experimented around for a couple of years with a 6' Fortec petal dish. On C-band, especially with a single orthomode feed, it was a good performer when very carefully tweaked. I could get nearly everything my larger dishes received, including DVB-S2. There were 1-2 FEC 9/10 DVB-S2 feeds that were on the edge and a small number of signals where the 6' couldn't discriminate adjacent orbital interference. However it became our workhorse C-band dish and spent most of its time on 58W where it got everything.

I had some success with the 6' on Ku, but in the end it rarely measured up to my 1.2m offsets. I tried a dual orthomode feed, both stock and with customizations for Ku, and an Invacom ADF-120 Ku-only feed with C120 flanged LNBs. The ADF-120 is truly an adjustable prime-focus feed, and it convinced me there was no future for Ku on my 6'. It didn't help that the 6' polar mount was pretty sloppy mechanically, and unable to grasp a 3" OD pole tightly enough to withstand the winds I endure.

Last week I retired the 6' because I got tired of climbing on the roof every time we had a wind storm. If it had been mounted in a better shielded location and the city ordinances allowed it, I would have continued to use it for C-band. Instead I put up a 2.6m Birdview prime-focus in a more accessible location on the roof. I have put a fair amount of time into adapting my dual ortho to work with this dish and am getting good results on both C and Ku (I have a thread about this in the C-band subforum). This is the first time I have a prime-focus dish beating my 1.2m offsets. The Birdview is alleged to have an accurate surface, however my 1.8m offset beats the 2.6m Birdview. This could be a limitation of the dual ortho feed. Someday I would like to test my ADF-120 on the Birdview and resolve this question once and for all.

 

[turbosat]

Agree with pendragon, go with the ku-band dish for less headaches. I don't know that they would "always outperform a c-band dish", a lot depends on the dish/mount, how accurate the parabolic shape is, how well it tracks, how much slop in the polar mount, etc.
I have a 10' SAMI dish, that rocks on ku, with the co-rotor feedhorn, but I don't use it for ku since I have 2 other steerable ku dish systems. Backups for backups , lol.